Attempts have been made to manufacture low cost, ambient-compensated current-actuated small circuit breakers, and particularly such devices which have relative freedom from chattering of the contacts, and good maintenance of contact pressure up to the point of contact separation. Almost invariably, the cost of such structures has been too high for wide acceptance by the mass markets, such as circuit breakers for the automobile industry. The reasons for this are many, but among them are the high cost of labor used in making the devices and the high cost of the materials of the circuit breaker. In addition, due to the vibration encountered in automobiles, and the wide range of ambient temperatures that automotive circuit breakers encounter during usage, it has been difficult to make satisfactory circuit breakers which are low enough in cost to sell in the automotive field.
In present day automobiles, for reasons of economy of installation and wiring, often a fuse panel will be installed which has on it many individual fuses. As to the panel, each fuse thereon requires two spring clips which must be riveted to the panel; and each fuse requires a body, end caps, and the fuse link itself. It takes many operations to assemble (from basic materials and parts) such a fuse and its clips. Again, labor costs for such steps tend to increase the cost of the finished panel and the fuses therefor.
It is known to use a thermostat metal blade to engage the end of a spring arm. The thermostat blade, when heated by current flowing therethrough, will bend in such manner as to release the spring arm so that the latter may move to open electrical contacts. However, in many such structures, there is no ambient compensation; and in most if not all such circuit breakers, contact pressure diminishes gradually as current passes through the device, thus permitting chattering of the contacts. Most of these designs in the prior art have been constructed in order to be serviceable on voltage circuits such as 110 v. A.C. or 220 v. A.C. Because of the requirements of the Underwriters Laboratory in respect to the performance of such devices, such prior art breakers are relatively expensive to construct and therefore costly to buy. As examples of these devices attention is drawn to the following U.S. Pat. Nos.: Jackson et al. 2,270,950; Frank et al. 2,320,355; Ingwersen 2,492,382; Millen 2,615,963; and Lombardo 2,844,690.
In addition, prior art devices in which a thermostatic blade must wipe across a spring arm during the circuit opening period, have the difficulty that the coefficient of friction between the spring arm and blade may vary from unit to unit, or may become variable during use. This gives rise to initial faulty calibration, or erratic calibration during use.